Up-converting and down-converting radio frequency (RF) carrier modulated signals is a common practice that is used in RF receivers and transmitters. Such up-converting and down-converting requires the RF carrier modulated signal to be re-modulated to a different RF carrier frequency. This process is performed by one of several techniques:
(1) the RF modulated signal can simply be de-modulated to baseband and re-modulated using a different RF carrier frequency;
(2) a Hilbert Transform process is used to convert a real modulated signal to a complex modulated signal and then modulate the signal with a complex carrier to the desired carrier frequency;
(3) a complex multiplier can be used to perform a first modulation and maintain the signal in complex form, successive modulations will modify the carrier frequency, the real part of the final modulation generates the desired re-modulated signal;
(4) an analog process can be used to re-modulate a real modulated signal carrier at, for example, a carrier fo with a real carrier at, for example, f1±fo and by using a filtering process to remove the undesired images at f1±(−fo);
(5) two techniques for re-modulating digital RF carrier modulated signals are disclosed in commonly assigned U.S. patent application Ser. No. 09/382,232, filed Aug. 24, 1999 and U.S. patent application Ser. No. 09/382,234, filed Aug. 24, 1999, both of which are in incorporated by reference.
Each of these techniques for re-modulating an RF carrier modulated signal either operate in the analog domain or require complex circuitry to implement the re-modulation process in the digital domain.
Therefore, there is a need in the art for a simple, digital process for re-modulating an RF carrier modulated signal.